1. Field of the Invention
The present invention relates to a method of decolorizing stock-raising treatment water discharged from a livestock barn or the like.
2. Description of the Related Art
With stock-raising treatment water discharged from a livestock barn (hereinafter referred to as ‘raw water’), a method is adopted in which the raw water is stored in a raw water tank, is fed therefrom into a solid-liquid separator using a pump, and is separated into a solid component such as feces and a liquid component, each of which is then treated. With a sieve shaker type or sloping screen type solid-liquid separation system that has been used with wastewater treatment apparatuses using a conventional activated sludge method, a sloping mesh screen is placed in a sloping opening of a hopper-like wastewater receiver, raw water containing excrement is fed using a pump onto an upper part of the sloping mesh screen, and is made to drop down along the sloping mesh screen, whereby a liquid component drops down through the mesh of the screen and is temporarily held in a filtrate tank from the hopper-like wastewater receiver, before being fed to the next treatment step, for example an aeration tank. The solid component, on the other hand, runs along the screen, and drops down into a solid component housing pitch from a lower edge of the screen and is accumulated. In the aeration tank, aeration is carried out with an aerator, and sludge in the wastewater is decomposed by activated sludge microbes. In general, a fixed type aerator is provided in the aeration tank, and minute bubbles are blown into the wastewater by this aerator, the inside of the tank is agitated at a fixed flow speed to make the dissolved oxygen concentration in the tank constant, and the activated sludge microbes are thus cultured so as to treat the wastewater.
Moreover, with conventional treatment equipment, decolorization treatment is carried out before the treated water is discharged into a public drain. Before color removal, the treatment liquid is a brown suspension, with the suspended matter containing fine fibrous matter, which clogs filters, and causes troublesome problems to remain in subsequent treatment. Conventional decolorization treatment involves an operation such as blowing in ozone, using a large amount of activated charcoal, or passing through an osmosis membrane, and to obtain a sufficient transparency, a considerable amount of ozone or activated charcoal and a considerable treatment time are required. Incidentally, with a method disclosed in Japanese Patent Application Laid-open No. 2003-205298 (‘Treatment apparatus for wastewater containing livestock urine’, laid open Jul. 22, 2003), as shown in FIG. 10, treatment water that has been treated in a membrane treatment part is sucked by a suction pump 142 and thus fed via a transfer pipe l15 into a filtrate water tank 108 that is provided next to a sludge storage tank 107 that is adjacent to a membrane separation tank 106, and then the filtered treatment water is fed into a decolorization treatment part 150 via a transfer pipe l16, and decolorization treatment is carried out to make the wastewater close to colorless and transparent. A decolorizer 150a constituting the decolorization treatment part 150 is constituted such that the treatment water that has been sucked from the filtrate water tank 108 is fed by a membrane supply high pressure pump 151 to a membrane module 152 having a reverse osmosis membrane, and the treatment water is decolorized by the reverse osmosis membrane which is washed with a chemical solution for washing by a chemical-injecting pump 154 from a chemical solution tank 153. In FIG. 10, l17 is a permeated liquid transfer pipe, l18 is a circulating water pipe, l19 is a concentrated water transfer pipe, and l20 is a washing water supply pipe. In this way, hitherto decolorization treatment has required large-scale equipment and a long treatment time, but even so sufficient effects have not been obtained.